The invention relates to an arched metal-ceramic substrate having one curred ceramic layer with a metal coating provided on both sides of the curved layer. The curved substrate having a convex shape in relation to a parallel planar axis.
Production of a metal coating required to produce printed conductors, terminals, etc. on a ceramic, for example an aluminum oxide ceramic using the so-called "DCB process" (direct copper bond technology) using metal or copper foils or metal or copper sheets which form the metal coating, and which have on their surface sides a layer or coating (fused layer) of a chemical compound of the metal and a reactive gas, preferably oxygen, is known. In this process, described for example in U.S. Pat. No. 3,744,120 or in DE-PS 2,319,854, this layer or this coating (fused layer) forms a eutectic with a melting point below the melting point of the metal (for example, copper) so that by placing the foil on the ceramic and by heating all the layers they can be joined to one another, by fusing the metal or copper essentially only in the area of the fused layer or oxide layer.
This DCB process, for example, has the following process steps:
oxidation of a copper foil such that a uniform copper oxide layer results; PA1 application of the copper foil to the ceramic layer; PA1 heating of the combination to a process temperature between roughly 1070 and 1075.degree. C., for example to roughly 1071.degree. C.; PA1 cooling to room temperature.
An arched substrate is known (EP 0 279 601) in which the metal layer on the top of the ceramic layer has a much greater thickness than the metal layer on the bottom of this substrate. This formation is also necessary, in the known case, since arching of the completed substrate after cooling is to be achieved using the DCB process, with which the two metal coatings are attached on the ceramic layer. Since the metal coating on the top has a greater thickness, thermally induced stresses on the top are greater than on the bottom, so that the substrate arches concavely on the top and convexly on the bottom during cooling. This "bimetal" effect is reversible, i.e., during heating. A bending back occurs so that when the known substrate is used for power components the contact pressure between the bottom of the substrate and the cooling body is reduced as heating increases, i.e., when a high contact pressure is necessary to achieve especially low heat transfer between the substrate and the cooling body.
The object of the invention is to devise a metal-ceramic substrate which is suitable for electrical or electronic power circuits or modules and which allows improved heat dissipation independent of temperature with simple and problem-free mounting in a housing.